Magnetic Element Having Low Saturation Magnetization

ABSTRACT

A magnetic device including a magnetic element is described. The magnetic element includes a fixed layer having a fixed layer magnetization, a spacer layer that is nonmagnetic, and a free layer having a free layer magnetization. The free layer is changeable due to spin transfer when a write current above a threshold is passed through the first free layer. The free layer is includes low saturation magnetization materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.11/843,496, filed Aug. 22, 2007, the entire contents of which areincorporated herein by reference.

BACKGROUND

This application relates to magnetic materials and structures having atleast one free ferromagnetic layer.

Various magnetic materials use multilayer structures which have at leastone ferromagnetic layer configured as a “free” layer whose magneticdirection can be changed by an external magnetic field or a controlcurrent. Magnetic memory devices may be constructed using suchmultilayer structures where information is stored based on the magneticdirection of the free layer.

One example for such a multilayer structure is a spin valve (SV) whichincludes at least three layers: two ferromagnetic layers and aconducting layer between the two ferromagnetic layers. Another examplefor such a multilayer structure is a magnetic or magnetoresistive tunneljunction (MTJ) which includes at least three layers: two ferromagneticlayers and a thin layer of a non-magnetic insulator as a barrier layerbetween the two ferromagnetic layers. The insulator for the middlebarrier layer is not electrically conducting and hence functions as abarrier between the two ferromagnetic layers. However, when thethickness of the insulator is sufficiently thin, e.g., a few nanometersor less, electrons in the two ferromagnetic layers can “penetrate”through the thin layer of the insulator due to a tunneling effect undera bias voltage applied to the two ferromagnetic layers across thebarrier layer.

Notably, the resistance to the electrical current across the MTJ or SVstructures varies with the relative direction of the magnetizations inthe two ferromagnetic layers. When the magnetizations of the twoferromagnetic layers are parallel to each other, the resistance acrossthe MTJ or SV structures is at a minimum value RP. When themagnetizations of the two ferromagnetic layers are anti-parallel witheach other, the resistance across the MTJ or SV is at a maximum valueRAP. The magnitude of this effect is commonly characterized by thetunneling magnetoresistance (TMR) in MTJs or magnetoresistance (MR) inSVs defined as (RAP-RP)/RP.

SUMMARY

This application discloses devices including magnetic elements thatinclude at least a fixed layer, a nonmagnetic spacer layer, and a freelow saturation magnetization layer. The spacer layer resides between thefixed and free layers. The magnetic element is configured to allow thefree layer to be switched using spin transfer when a write current ispassed through the magnetic element.

In some implementations, the magnetic element further includes a secondspacer layer and a second fixed layer. In other aspects, the magneticelement further includes a second spacer layer, a second fixed layer anda second free layer magnetostatically coupled to the free layer.

One or more of the free layers are configured to have low saturationmagnetization. In certain implementations, one or more of the freelayers could include ferromagnetic material(s) combined with nonmagneticmaterial(s) In certain implementations the nonmagnetic material(s)include at least one of Zr, Ta, Nb, Mo, Re, W, Ti, V, Cr and Hf. Incertain implementations the nonmagnetic materials include at least twononmagnetic materials X and Y; where X includes at least one of Ti, Zr,and Hf; and Y includes at least one of V, Nb, Ta, Cr, Mo, W, and Re.

In certain implementations, one or more of the spacer layer(s) couldinclude insulating layers or conducting layers. In certainimplementations, one or more of the free layer(s) or fixed layer(s)could be synthetic. In certain implementations, the magnetic elementcould include a high spin polarization layer residing next to one ormore free layer. In certain implementations, the composition of theferromagnetic material(s) combined with nonmagnetic material(s) iscontrolled to provide low magnetostriction.

Some of the disclosed implementations may have the advantages of anamorphous structure that can contribute to lowering switching current,low saturation magnetization that can contribute to lowering switchingcurrent, low magnetostriction that can contribute to reducing switchingcurrent variability, or induced perpendicular anisotropy that cancontribute to reducing switching current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a magnetic element in the form a spin valve.

FIG. 1B is a diagram of magnetic element in the form of a spin tunnelingjunction.

FIG. 2A depicts a first implementation, a portion of a magnetic elementhaving a low saturation magnetization free layer.

FIG. 2B depicts another implementation, a portion of a magnetic elementutilizing a conducting spacer layer having a low saturationmagnetization free layer.

FIG. 2C depicts another implementation, a portion of a magnetic elementutilizing an insulating spacer layer having a low saturationmagnetization free layer.

FIG. 2D depicts another implementation, a portion of a magnetic elementutilizing a high spin polarization layer having a low saturationmagnetization free layer.

FIG. 2E depicts implementation, a portion of a magnetic elementutilizing a low saturation magnetization fixed layer having a lowsaturation magnetization free layer.

FIG. 2F depicts another implementation, a portion of a magnetic elementutilizing a synthetic fixed layer having a low saturation magnetizationfree layer.

FIG. 2G depicts another implementation, a portion of a magnetic elementutilizing a synthetic free layer having a low saturation magnetizationfree layer.

FIG. 3A depicts another implementation, a magnetic element having a lowsaturation magnetization free layer.

FIG. 3B depicts another implementation, a magnetic element having a lowsaturation magnetization free layer.

FIG. 4 depicts another implementation, a magnetic element having a lowsaturation magnetization free layer.

FIG. 5 depicts another implementation, a magnetic element having a lowsaturation magnetization free layer.

FIG. 6 depicts another implementation, a device having a low saturationmagnetization free layer.

FIG. 7 depicts one implementation, a magnetic element having a lowsaturation magnetization free layer connected to a bit line and anisolation device.

FIG. 8 depicts one implementation of the device in FIG. 7 illustrating acircuit that operates the device based on spin-transfer torque switchingwith low saturation magnetization.

DETAILED DESCRIPTION

FIGS. 1A and 1B depict magnetic elements 10 and 10′. The magneticelement 10 is a spin valve and includes a antiferromagnetic (AFM) layer12, a fixed layer 14, a conductive spacer layer 16 and a free layer 18.Other layers (not shown), such as seed or capping layer can also beused. The fixed layer 14 and the free layer 18 are ferromagnetic. Thefree layer 18 is depicted as having a changeable magnetization 19. Themagnetization of the free layer 18 is free to rotate, typically inresponse to an external magnetic field. The conductive spacer layer 16is nonmagnetic. The AFM layer 12 is used to pin the magnetization of thefixed layer 14 in a particular direction. After post annealing, theferromagnetic layer 14 is pinned with a fixed magnetization 15. Alsodepicted are top contact 20 and bottom contact 22 that can be used todrive current through the magnetic element 10.

The magnetic element 10′ depicted in FIG. 1B is a magnetic tunnelingjunction. Portions of the magnetic tunneling junction 10′ are analogousto the spin valve 10. Thus, the magnetic element 10′ includes an AFMlayer 12′, a fixed layer 14′ having a fixed layer magnetization 15′, ainsulating barrier layer 16′, a free layer 18′ having a changeablemagnetization 19′. The barrier layer 16′ is thin enough for electrons totunnel through in a magnetic tunneling junction 10′.

The relationship between the resistance to the current flowing acrossthe MTJ or SV and the relative magnetic direction between the twoferromagnetic layers in the TMR or MR effect can be used for nonvolatilemagnetic memory devices to store information in the magnetic state ofthe magnetic element. Magnetic random access memory (MRAM) devices basedon the TMR or MR effect, for example, can be an alternative of andcompete with electronic RAM devices. In such devices, one ferromagneticlayer is configured to have a fixed magnetic direction and the otherferromagnetic layer is a “free” layer whose magnetic direction can bechanged to be either parallel or opposite to the fixed direction andthus operate as a recording layer. Information is stored based on therelative magnetic direction of the two ferromagnetic layers on two sidesof the barrier of the MTJ or SV. For example, binary bits “1” and “0”can be recorded as the parallel and anti-parallel orientations of thetwo ferromagnetic layers in the MTJ or SV. Recording or writing a bit inthe MTJ or SV can be achieved by switching the magnetization directionof the free layer, e.g., by a writing magnetic field generated bysupplying currents to write lines disposed in a cross stripe shape, by acurrent flowing across the MTJ or SV based on the spin transfer effect,or by other means.

In spin-transfer switching, the current required for changing themagnetization of the free layer can be significantly less than thecurrent used for the field switching. Therefore, the spin-transferswitching in a MTJ or SV can be used to significantly reduce the powerconsumption of the cell. However, the write current that causesspin-transfer switching can lead to design problems for high densityMRAM, such as heating, high power consumption, large transistor size, aswell as other issues. Moreover, if an MTJ is used a high write currentcan lead to a degradation of the insulating barrier. Accordingly, whatis needed is a magnetic element having magnetic layers that can beswitched using spin transfer at a lower current density that consumesless power.

This application describes magnetic devices including a magnetic elementhaving at least one low saturation magnetization free ferromagneticlayer that can be switched with the spin transfer effect.

FIG. 2A depicts one implementation, a magnetic element 100 having a lowsaturation magnetization free layer. The magnetic element 100 includes afixed layer 110, a spacer layer 120, and a free layer 130. As describedbelow, the free layer 130 is configured to have a low saturationmagnetization. Furthermore, the magnetic element 100 is configured suchthat the free layer 130 can be written using spin transfer.

FIG. 2B depicts a magnetic element 100′ that is analogous to themagnetic element 100. Thus, analogous components are labeled similarly.The magnetic element 100′, therefore, includes a free layer 130′ thatcan be written using spin transfer and that has a low saturationmagnetization. The magnetic element 100′ also includes a fixed layer110′. However, the magnetic element 100′ includes a conducting spacerlayer 120′.

FIG. 2C depicts a magnetic element 100″ that is analogous to themagnetic element 100. Like the magnetic element 100, the magneticelement 100″ includes a fixed layer 110″ having a fixed layermagnetization 111″ and a free layer 130″ with a low saturationmagnetization 131″ that can be written using spin transfer. However, themagnetic element 100″ includes a insulating spacer layer 120″.

FIG. 2D depicts a magnetic element 100′″ that is analogous to themagnetic element 100. Like the magnetic element 100, the magneticelement 100′″ includes a fixed layer 110′″ having a fixed layermagnetization 111′″, a spacer layer 120′″, and a free layer 130′″ with alow saturation magnetization 131′″ that can be written using spintransfer. The magnetic element 100′″ further includes a high spinpolarization layer 140 residing between the spacer layer 120′″ and freelayer 130′″. A high spin polarization material has higher spinpolarization than the adjacent ferromagnetic layer. The high spinpolarization layer 140, such as CoFe three to eight angstroms thick,resides at the interface between the free layer 130′″ and the spacerlayer 120′″ and increases magnetoresistance and spin torque.

FIG. 2E depicts a magnetic element 100″″ that is analogous to themagnetic element 100. Like the magnetic element 100, the magneticelement 100″″ includes a fixed layer 110″″ having a fixed layermagnetization 111″″, a spacer layer 120″″, and a free layer 130″″ havinga free layer magnetization 131″″ that can be written using spintransfer. Both the fixed layer 110″″ and the free layer 130″″ includelow saturation magnetization materials.

FIG. 2F depicts a magnetic element 100′″″ that is analogous to themagnetic element 100. Like the magnetic element 100, the magneticelement 100′″″ includes a spacer layer 120′″″ and a free layer 130′″″with a low saturation magnetization 131′″″ that can be written usingspin transfer. The magnetic element 100′″″ also includes a syntheticfixed layer 110′″″ that includes a fixed layer 144 with a fixed layermagnetization 145, a nonmagnetic layer 140, and a fixed layer 136 with afixed layer magnetization 137. An antiferromagnetic layer (not shown)can be included to pin the magnetization of the fixed layer 136 in adesired direction after post annealing. The nonmagnetic layer 140preferably includes Ru and is configured such that the fixed layermagnetizations 137 and 145 are antiparallel.

FIG. 2G depicts a magnetic element 100″″″ that is analogous to themagnetic element 100. Like the magnetic element 100, the magneticelement 100″″″ includes a fixed layer 110″″″ with a saturationmagnetization 111″″″ and a spacer layer 120″″″. The magnetic 100″″″element also includes a synthetic free layer 130″″″ with low saturationmagnetization that that can be written using spin transfer. The freelayer 130″″″ includes a free layer 160 with a magnetization 161, anonmagnetic layer 164, and a free layer 168 with magnetization 169. Thenonmagnetic layer 164 can include Ru and is configured such that themagnetization of layers 160 and 168 are antiparallel.

The magnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″can be used in various devises such as magnetic memory. The magneticelements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ can be usedin a memory cell including an isolation transistor (not shown), as wellas other configurations of magnetic memories. Moreover, the magneticelements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ can utilizetwo terminals (not shown) near the top and bottom of the magneticelement. The magnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″,and 100″″″ can use another number of terminals, for example a thirdterminal near the center of the magnetic element. The magnetic elements100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ can also include anAFM layer (not shown) used to pin the magnetization of the fixed layers110, 110′, 110″, 110′″, 110″″, 136, and 110″″″, as well as seed layers(not shown) and capping layers (not shown). Furthermore, the magneticelements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ areconfigured such that the free layers 130, 130′, 130″, 130′″, 130″″,130′″″, and 130″″″ can be written using spin transfer.

For magnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″,some difference can be provided between the lateral dimensions ofelements to ensure that the free layer 130, 130′, 130″, 130′″, 130″″,130′″″, and 130″″″ has a particular easy axis in the plane of the freelayer.

Referring to FIG. 2A, for clarity, the discussion below primarily refersto the free layer 130. However, free layers 130′, 130″, 130′″, 130″″,130′″″, and 130″″″ can be provided in a similar manner as that describedfor the free layer 130. Moreover, other magnetic layers within elements100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ can also be providedin a similar manner as that described for free layer 130.

Referring back to FIG. 2A, the low saturation magnetization can beprovided by providing a free layer that includes a ferromagneticmaterial and nonmagnetic material. To obtain low saturationmagnetization for the free layer 130, a ferromagnetic material and anonmagnetic material can be combined in a single ferromagnetic layerused in or for the free layer 130. Thus, the low saturationmagnetization free layer 130 can be made by combining ferromagnetic andnonmagnetic materials.

For example, a low saturation magnetization free layer 130 can beprovided by combining ferromagnetic material Co, Fe, Ni, or one of theiralloys with at least Zr, W, Ti, V, or Hf. In one implementation, theelements Zr, W, Ti, V, or Hf are in the range of five through fiftyatomic percent. In another implementation, a low saturation free layer130 can be provided by combining ferromagnetic material Co, Fe, Ni, orone of their alloys with at least two nonmagnetic materials X and Ywhere X includes Ti, Zr, or Hf and Y includes V, NB, Ta, Cr, Mo, W, orRe. In one implementation, the sum of the materials X and Y are in therange of five through fifty atomic percent. In another implementation, alow saturation magnetization free layer 130 can be provided by combiningferromagnetic material Co, Fe, Ni, or one of their alloys with at leastZr and Ta. In one implementation, the sum of Zr and Ta are in the rangeof five through fifty atomic percent.

Because the current required to switch a magnetic element by the spintransfer effect increases with increasing magnetization of the freelayer, combining the ferromagnetic material(s) with nonmagneticmaterials(s) can provide the benefit of lowering the spin transferswitching current.

Some implementations can have the benefit of promoting an amorphousstructure during magnetic layer deposition that can have the additionalbenefit of lowering the spin transfer switching current. An amorphousstructure can also have the benefit of increasing TMR and MR.

An annealing process can crystallize some amorphous magnetic basedalloys. In the implementation utilizing a low saturation magnetizationfree layer 130 that is provided by doping ferromagnetic material Co, Fe,Ni, or one of their alloys with at least Zr and Ta ranging between 5 and50 atomic percent an annealing process can cause the free layer 130 tocrystallize. In one implementation, the atomic percentage of Zr isgreater than the atomic percentage of Ta, the free layer is in the hcpor fcc crystal structure after annealing, and the free layer 130 has aperpendicular anisotropy so that it magnetization 131 is perpendicularto the plane of the free layer. Utilizing materials that provide aperpendicular anisotropy can provide a benefit of a lower switchingcurrent compared to an in plane anisotropy. In another implementation,the atomic percentage of Zr is less than the atomic percentage of Ta andthe free layer is in the bcc crystal structure after annealing.

Controlling the composition of the free layer can control themagnetostriction of the magnetic element. For example, in the case of Codoped with Ti, Zr, or Hf the magnetostriction is positive. In the caseof Co doped with V, Nb, Ta, Cr, Mo, W, or Re the magnetostriction isnegative. By controlling the ration of X and Y a magnetic element can beprovided with low magnetostriction. Lowering the magnetostriction canhave the benefit of lowering the variability of the switching current insome implementations. In one implementation a low saturationmagnetization free layer 130 is provided by combining ferromagneticmaterial Co, Fe, Ni, or one of their alloys with at least twononmagnetic materials X and Y where X includes Ti, Zr, or Hf and Yincludes V, NB, Ta, Cr, Mo, W, or Re such that the ratio of X and Y iscontrolled to achieve low magnetostriction.

Thus, the magnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″, and100″″″ include the free layers 130, 130′, 130″, 130′″, 130″″, 130′″″,and 130″″″, respectively, having a low saturation magnetization asdefined above. Consequently, some of the implementations of the magneticelements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ can bewritten using spin transfer at a lower switching current. By controllingthe composition of the magnetic elements some implementations canachieve additional benefits such as perpendicular anisotropy, amorphousstructure, or low magnetostriction.

FIG. 3A depicts another implementation of a magnetic element 200 havinga low saturation magnetization free layer. The magnetic element includesa fixed layer 210 with a fixed layer magnetization 211, a spacer layer220, a free layer 230 with a free layer magnetization 231, a spacerlayer 240, and a fixed layer 250 with a fixed layer magnetization 251.

In one implementation the spacer layer 220 is insulating and the spacerlayer 240 is conducting. In such an implementation the magnetic element200 includes a spin valve portion 204 and a magnetic tunneling junctionportion 202 that share the free layer 230. Referring to FIGS. 2A and 4,the layers 250, 240, and 230 are analogous to the layers 110, 120, and130 in the magnetic element 100 when the spacer layer 120 is conducting.Similarly, the layers 210, 220, and 230 are analogous to the layers 110,120, and 130, respectively, when the spacer layer 120 is an insulatingbarrier layer. The fixed layers 210 and 250 thus correspond to the fixedlayer 110 and can be configured using analogous materials, layers,and/or process. The free layer 230 is configured to be written usingspin transfer and has a low saturation magnetization. The magneticelement 200 can include pinning layers (not shown) and can includeantiferromagnetic layers, that pin the fixed layers 210 and 250.Moreover, the magnetic element 200 can utilize two terminals (not shown)near the top and bottom of the magnetic element. Further, the magneticelement 200 can include another number of terminals, for example a thirdterminal near the center of the magnetic element 200.

The free layer 230 can be configured in a manner analogous to the freelayers 130, 130′, 130″, 130′″, 130″″, 130′″″, and/or 130″″″. Thus,analogous materials and principles to those discussed above can be usedto achieve the low saturation magnetization of the free layer 230. Forexample, the combination of ferromagnetic materials with nonmagneticmaterials can be used to achieve a low saturation magnetization for thefree layer 230. The magnetic element 200 can share the benefits of themagnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″, andtheir combinations. Furthermore, when the fixed layers 210 and 250 arealigned antiparallel, both the spin valve portion 204 and the magnetictunneling junction portion 202 can contribute to writing the free layer230. Because of the use of the barrier layer 220, the magnetic element200 can have a higher resistance and magnetoresistance. Consequently, ahigher signal can be obtained during reading.

Further, the spacer layer 220 and spacer layer 240 of the magneticelement 200 can be both insulating or both conducting. FIG. 3B depicts amagnetic element 200′ that is analogous to the magnetic element 200.Like the magnetic element 200, the magnetic element 200′ includes afixed layer 210′ with a fixed layer magnetization 211′, a free layer230′ having a low saturation magnetization 231′ that can be switched dueto spin transfer, and a fixed layer 250′ with a fixed layermagnetization 251′. The magnetic element 200′ also includes aninsulating layer 220′ that is analogous to the spacer layer 220 and aninsulating layer 240′ that is analogous to the spacer layer 240.

The free layer 230′ can be configured in a manner analogous to the freelayers 130, 130′, 130″, 130′″, 130″″, 130′″″, and/or 130″″″. Thus,analogous materials and principles to those discussed above can be usedto achieve the low saturation magnetization of the free layer 230′. Forexample, combining ferromagnetic with nonmagnetic materials can be usedto achieve a low saturation magnetization for the free layer 230′. Themagnetic element 200 can share the benefits of the magnetic elements100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″, and theircombinations. Furthermore, when the fixed layers 210′ and 250′ arealigned antiparallel, both the spin valve portion 204 and the magnetictunneling junction portion 202 can contribute to writing the free layer230.

FIG. 4 depicts another implementation of a portion of a magnetic element300 having a low saturation magnetization free layer. The magneticelement includes a structure 302 and a structure 304, each of which isanalogous to the magnetic element 100, 100′, 100″, 100′″, 100″″, 100″″″,or 100′″″″. Thus, the structure 302 includes a fixed layer 310, a spacerlayer 320, and a free layer 330 that are analogous to, for example, thelayers 110, 120, and 130, respectively, of the magnetic element 100. Thestructure 302 also includes a pinning layer 306 that can be an AFMlayer. Similarly, the structure 304 includes a fixed layer 370, a spacerlayer 360, and a free layer 350 that are analogous to, for example, thelayers 110, 120, and 130, respectively, of the magnetic element 100. Thestructure 304 also includes pinning layer 380 that can be an AFM layer.One or both of the free layers 330 and 350 have a low saturationmagnetization. Furthermore, the free layers 330 and 350 of the magneticelement 300 are magnetostatically coupled. The magnetostatic couplingcan be configured so that the layers 330 and 350 areantiferromagnetically aligned. In the implementation shown, the magneticelement 300 includes a separation layer 340. The separation layer 340 isconfigured to ensure that the free layers 330 and 350 are onlymagnetostatically coupled. For example, the thickness of the separationlayer 340, which can be a nonmagnetic conductor, can be configured toensure that the free layers 330 and 350 are antiferromagneticallyaligned due to a magnetostatic interaction. The separation layer 340 canserve to randomize the polarization of the spins passing through it. Forexample, the separation layer 340 includes materials such as Cu, Ag, Au,Pt, Mn, CuPt, CuMn, a Cu/Pt/Cu sandwich, a Cu/Mn/Cu sandwich, or aCu/PtMn[1-20A]/Cu sandwich.

The free layer 330 and/or the free layer 350 are configured to have alow saturation magnetization, as defined above. Thus, the free layer 330and/or 350 can correspond to the free layers 130, 130′, 130″, 130′″,130″″, 130′″″, or 130″″″. The materials and/or properties used in thefree layer 330 and/or the free layer 350 can be the same as or analogousto those described above with respect to the magnetic elements 100,100′, 100″, 100′″, 100″″, 100′″″, or 100″″″. Thus, the magnetic element300 can share many of the benefits of the magnetic elements 100, 100′,100″, 100′″, 100″″, 100′″″, or 100″″″. In particular, the magneticelement can be written using spin transfer at a lower switching currentdensity.

The magnetostatic coupling between the free layers 330 and 350 can beimplemented to provide further benefits. Because the free layers 350 and330 are magnetostatically coupled, a change in magnetization of the freelayer 350 can be reflected in the free layer 330. The spacer layer 320can be replaced with a barrier layer to provide a high signal.Furthermore, because they have separate free layers 350 and 330 theproperties of the spin valve 304 and the magnetic tunneling junction302, respectively, can be separately controlled to improve theirfunctions of the spin valve and spin tunneling junction, respectively.

FIG. 5 depicts another implementation of a magnetic element 400 having areduced low saturation magnetization free layer. The magnetic element400 is analogous to the magnetic element 300 depicted in FIG. 4. Thus,analogous components are labeled similarly. Therefore, the magneticelement includes a free layer 430 and a free layer 450, whichcorresponds to the free layers 330 and 350, respectively, either or bothof which has low saturation magnetization, and both of which are writtenusing spin transfer. Moreover, the magnetic element 400 can utilize twoterminals (not shown) near the top and bottom of the magnetic element.However, the magnetic element can use another number of terminals, forexample a third terminal near the center of the magnetic element 400.

The magnetic element 400 includes a synthetic fixed layer 410 and asynthetic fixed layer 470. The fixed layer 410 includes a ferromagneticlayers 412 416 separated by a nonmagnetic layer 414 that can be Ru. Themagnetizations of the ferromagnetic layers 412 and 416 are also alignedantiparallel. Similarly, the fixed layer 470 includes ferromagneticlayers 472 and 476 separated by a nonmagnetic layer 474 that can be Ru.The magnetizations of the ferromagnetic layers 472 and 476 are alsoaligned antiparallel. Furthermore, a spacer layer 420 can be a barrierlayer that is insulating yet allows electrons to tunnel between theferromagnetic layer 416 and the a free layer 430. The spacer layer 460can be a conductive layer. Thus, the structure 402 is a spin tunnelingjunction, while the structure 404 is a spin valve.

The free layers 430 and/or 450 can be configured in a manner analogousto the free layers 130, 130′, 130″, 130′″, 130″″, 130′″″, 130″″″ or thefree layers 330 and 350, respectively. Thus, analogous materials andprinciples to those discussed above can be used to achieve the lowsaturation magnetization of the free layers 430 and/or 450. For example,combination of ferromagnetic materials with nonmagnetic materials can beused to achieve a low saturation magnetization for the free layer 430and/or 450. Because of the low saturation magnetization, the magneticelement 500 can be written using spin transfer at a lower switchingcurrent density. The magnetic element 500 can share the benefits of themagnetic elements 100, 100′, 100″, 100′″, 100″″, 100′″″, and 100″″″ andtheir combinations.

Furthermore, because the free layers 430 and 450 are magnetostaticallycoupled, a change in magnetization direction of the free layer 450, forexample due to spin transfer induced writing, can be reflected in themagnetization of the free layer 430. With the barrier layer 420, themagnetic tunneling junction 402 can provide a high signal. In anotherimplementation, the barrier layer 420 can be replaced by a conductinglayer. However, in such an implementation, the read signal can decreasefor a given read current.

In one implementation the magnetic element 400 can be configured suchthat the magnetizations of the ferromagnetic layer 412 and theferromagnetic layer 476 are parallel. Because the ferromagnetic layers412 and 476 have their magnetizations aligned parallel, the AFM layers406 and 480 can be aligned in the same direction. The AFM layers 406 and480 can, therefore, be aligned in the same step. Thus, processing isfurther simplified.

Some of the implementations of the magnetic elements 100, 100′, 100″,100′″, 100″″, 100′″″, 100″″″, 200, 300 and 400 can achieve the benefitsof low spin transfer switching current, low magnetostriction, amorphousgrowth, and perpendicular anisotropy.

FIG. 6 depicts another implementation, a device 500 having an array ofmagnetic elements having at least one low magnetization free layer andhaving a low saturation magnetization free layer. The device 500includes a an array of magnetic elements 510. Each magnetic element 510includes at least a fixed layer, a spacer layer, and a free layer havinga low saturation magnetization as described above. Magnetic elements 510can include the principles seen in magnetic elements 100, 100′, 100″,100′″, 100″″, 100′″″, 100″″″, 200, 300, 400, or a combination of thoseelements. The device 500 can have isolation transistors (not shown),read and write lines (not shown), and logic circuitry (not shown) foraccessing individual magnetic elements. The device 500 can be used inmagnetic memory systems.

FIG. 7 depicts another implementation, a device 700 having a magneticelement 701 based on the spin-transfer torque effect having at least onelow magnetization free layer. A conductor line 710 labeled as “bit line”is electrically coupled to the magnetic element 701 by connecting to oneend of the magnetic element 701 to supply an electrical drive current740 through the layers of the magnetic element 701 to effectuate thespin-transfer torque effect in the magnetic element 701. An electronicisolation device 730, such as an isolation transistor, is connected toone side of the magnetic element 701 to control the current 740 inresponse to a control signal applied to the gate of the transistor 730.A second conductor line 720 labeled as “word line” is electricallyconnected to the gate of the transistor 730 to supply that controlsignal. In operation, the drive current 740 flows across the layers inthe magnetic element 701 to change magnetization direction of the freelayer when the current 740 is greater than a switching threshold whichis determined by materials and layer structures of the magnetic element701. The switching of the free layer in the magnetic element 701 isbased on the spin-transfer torque caused by the drive current 740 alonewithout relying on a magnetic field produced by the lines 710 and 720 orother sources.

In various applications, the magnetic cell shown in FIG. 7 isimplemented as a unit cell of a magnetic array. FIG. 8 shows a bird viewof an example of such an array formed on a substrate as an integratedcircuit chip. FIG. 8 shows one implementation of the device in FIG. 7illustrating a circuit that operates the device based on spin-transfertorque switching. Each magnetic cell contains at least one lowmagnetization free layer and is operated based on the spin-transfertorque switching. The cells 810 can be arranged and connected in anarray in a common way without special requirement for the bit/sourcelines. Each cell 810 is connected in series to a select transistor 820which corresponds to the isolation device 730 in FIG. 2. As illustrated,a bit line selector 801, a source line selector 802 and a word lineselector 803 are coupled to the cell array to control the operations ofeach cell.

Magnetic elements have been described that include a low saturationmagnetization free layer and can be written using spin. While thespecification of this application contains many specifics, these shouldnot be construed as limitations on the scope of any invention or of whatmay be claimed, but rather as descriptions of features specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

Only a few examples are described. One of ordinary skill in the art canreadily recognize that variations, modifications and enhancements to thedescribed examples may be made.

1. A device comprising: one or more magnetic memory cells, each one ofthe magnetic memory cells including: a magnetic element including: afirst fixed layer having a fixed layer magnetization; a first spacerlayer that is nonmagnetic; and a first free layer having a free layermagnetization that is changeable due to spin transfer when a writecurrent above a threshold is passed through the first free layer; thefirst spacer layer residing between the first fixed layer and the firstfree layer, the first free layer including at least one ferromagneticmaterial and at least one nonmagnetic material, wherein the at least onenonmagnetic material is selected from a group consisting of W, Ti, V,and Hf to lower the threshold of the write current for the first freelayer including the at least one nonmagnetic material compared to thefirst free layer not including the at least one nonmagnetic material;and a circuit comprising at least an isolation transistor electricallyconnected to the magnetic element to control the write current throughthe magnetic element.
 2. The device of claim 1, wherein theferromagnetic material of the first free layer includes at least one ofCo, Ni, or Fe.
 3. The device of claim 1, wherein the ferromagneticmaterial of the first free layer includes at least one of alloy of CoNi,CoFe, NiFe, or CoNiFe.
 4. The device of claim 1, wherein the first freelayer includes at least five atomic percent and less than or equal tofifty atomic percent W, Ti, V, or Hf.
 5. The device of claim 1, whereinthe first spacer layer includes an insulating material.
 6. The device ofclaim 5, wherein the insulating material includes Al₂O₃ or MgO.
 7. Thedevice of claim 1, wherein the first spacer layer includes a conductinglayer.
 8. The device of claim 7, wherein the conducting layer includesat least one of Ru, Re, Cu, Ta or Cu, and an alloy that includes Ru, Re,Cu, Ta or Cu.
 9. The device of claim 1, wherein the first fixed layerincludes at least one ferromagnetic material and at least onenonmagnetic material, and the nonmagnetic material includes at least oneof W, Ti, V, or Hf.
 10. The device of claim 1, wherein the magneticelement further comprises: a second spacer layer that is nonmagnetic,the first free layer residing between the second spacer layer and thefirst spacer layer; and a second fixed layer, the second spacer layerresiding between the second fixed layer and the first free layer. 11.The device of claim 10, wherein the first spacer layer includes aninsulating material and the second spacer layer includes an insulatingmaterial.
 12. The device of claim 10, wherein the first spacer layerincludes a conducting material and the second spacer layer includes aninsulating material.
 13. The device of claim 1, wherein the magneticelement further comprises: a first separation layer, the first freelayer residing between the first spacer layer and the first separationlayer; a second free layer having a free layer magnetization that ischangeable due to a magnetic field created by the first free layer, thefirst separation layer residing between the first free layer and thesecond free layer; a second spacer layer that is nonmagnetic, the secondfree layer residing between the second spacer layer and the firstseparation layer; and a second fixed layer having a fixed layermagnetization, the second spacer layer residing between the second fixedlayer and the second free layer.
 14. The device of claim 1, comprising aplurality of the magnetic memory cells.
 15. The device of claim 1,further comprising: a conductor line; and a plurality of the magneticmemory cells, each magnetic memory cell being electrically connected tothe conductor line to receive the write current.